74 A NATURALIST IN TASMANIA ch. 



for the district looks after a small accommodation 

 hut for travellers, a few enthusiastic fishermen, 

 and shepherds. All round the flanks of the tiers, 

 which gradually ascend to the plateau, lie the 

 Palaeozoic sandstone strata intersected by dykes 

 of greenstone ; the sandstones become rarer and 

 rarer as we ascend, until on the tops of the tiers, 

 and on the topmost plateau, it is all greenstone, 

 except for a few small patches of sandstone, 

 which show that at one time the whole region 

 was covered by these deposits, but has been 

 subsequently denuded. The greenstone or dia- 

 base, which composes so much of the central and 

 eastern part of Tasmania and forms the charac- 

 teristic flat tablelands on the tops of all the 

 mountains, is an igneous but not a true eruptive 

 rock ; that is to say, it was thrust upwards or 

 possibly thrust in sidewards as a sill, without 

 attaining to the surface, and solidified under the 

 pressure of the overlaying strata. This volcanic 

 disturbance took place after the Palaeozoic marine 

 sandstones had been deposited, as is witnessed 

 by the alteration of these latter strata, where 

 they come into contact with the greenstone, and 

 it was probably to a great extent the agency 

 by which the centre and east of Tasmania was 

 raised permanently above the sea in late Palaeo- 

 zoic times. The age of the sand- and mud-stone 

 strata is roughly correlated with the Permian and 

 Carboniferous of Europe, the characteristic fossils 

 being such forms as the large Brachiopod shell. 



